1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to radio frequency identification (RFID) communication systems including RFID readers that communicate with RFID tags.
2. Background Art
Radio frequency identification (RFID) tags are electronic devices that may be affixed to items whose presence is to be detected and/or monitored. The presence of an RFID tag, and therefore the presence of the item to which the tag is affixed, may be checked and monitored wirelessly by devices known as “readers.” Readers typically have one or more antennas transmitting radio frequency signals to which tags respond. Since the reader “interrogates” RFID tags, and receives signals back from the tags in response to the interrogation, the reader is sometimes termed as “reader interrogator” or simply “interrogator”.
In a RFID system, typically a reader transmits a continuous wave (CW) or modulated radio frequency (RF) signal to a tag. The tag receives the signal, and responds by modulating the signal, “backscattering” an information signal to the reader. The reader receives signals back from the tag, and the signals are demodulated, decoded and further processed.
With the maturation of RFID technology, efficient communications between tags and readers has become a key enabler in supply chain management, especially in manufacturing, shipping, and retail industries, as well as in building security installations, healthcare facilities, libraries, airports, warehouses etc.
Physically locating a specific tag in a population of tags is difficult. This is because readers typically have a reading range of terms of feet, and thus many tags may respond to interrogation signals of a reader at any one time. When multiple tags are within a communication range of a reader, a single tag cannot be physically distinguished from the other tags. Thus, what is desired are ways of physically locating specific tags within groups of tags.